function  GeneRegulation_Nullcline_with_Jacobian ( a , b )

ux = 0:0.001:4;
vx = 0:0.001:4;
u = a./(1+vx.^b);
v = a./(1+ux.^b);

figure;
plot(ux,v,'g');
hold on;
plot(u,vx,'m');
xlabel('u','FontSize',12);ylabel('v','FontSize',12);
title({'a=' a},'FontSize',15);
axis([0 4 0 4]);

% find equilibrium points, calculate their jacobi matrix
if a==1  % one equilibrium point
    [uc vc] = Find_StablePoint ( a, b, 0.7, 0.6 );
    MyJacobian(a, b, uc,vc );
elseif a==2  % one equilibrium point
    [uc vc] = Find_StablePoint ( a, b, 1.5, 0.5 );
    MyJacobian(a, b,  uc,vc );
elseif a==3  % one equilibrium points
    [uc vc] = Find_StablePoint ( a, b, 0.5, 0 );
    MyJacobian(a, b,  uc,vc );
    [uc vc] = Find_StablePoint ( a, b, 1.2, 1.3 );
    MyJacobian(a, b,  uc,vc );
    [uc vc] = Find_StablePoint ( a, b, 3, 2.5 );
    MyJacobian(a, b,  uc,vc );
end

end

